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11.
Capillary reversed-phase high-performance liquid chromatography (RP-HPLC) utilizing monolithic poly(styrene-divinylbenzene) columns was optimized for the coupling to electrospray ionization mass spectrometry (ESI-MS) by the application of various temperatures and mobile phase additives during peptide and protein analysis. Peak widths at half height improved significantly upon increasing the temperature and ranged from 2.0 to 5.4 s for peptide and protein separations at 70 degrees. Selectivity of peptide elution was significantly modulated by temperature, whereas the effect on proteins was only minor. A comparison of 0.10% formic acid (FA), 0.050% trifluoroacetic acid (TFA), and 0.050% heptafluorobutyric acid (HFBA) as mobile phase additives revealed that highest chromatographic efficiency but poorest mass spectrometric detectabilities were achieved with HFBA. Clusters of HFBA, water, and acetonitrile were observed in the mass spectra at m/z values >500. Although the signal-to-noise ratios for the individual peptides diverged considerably both in the selected ion chromatograms and extracted mass spectra, the average mass spectrometric detectabilities varied only by a factor of less than 1.7 measured with the different additives. Limits of detection for peptides with 500 nl sample volumes injected onto a 60 mm x 0.20 mm monolithic column were in the 0.2-13 fmol range. In the analysis of hydrophobic membrane proteins, HFBA enabled highest separation selectivity at the cost of lower mass spectral quality. The use of 0.050% TFA as mobile phase additive turned out to be the best compromise between chromatographic and mass spectrometric performance in the analysis of peptides and proteins by RP-HPLC-ESI-MS using monolithic separation columns. 相似文献
12.
Gunter Silber Dieter Flockerzi Rajendra Singh Varma Ramamurthy Charubala Eugen Uhlmann Wolfgang Pfleiderer 《Helvetica chimica acta》1981,64(5):1704-1716
Nucleotides. XV. Synthesis and Properties of 2′O-t-Butyldimethylsilyl-5′-O-monomethoxytritylribonucleoside-3′-phosphotriesters, Starting Materials for Oligonucleotide Syntheses The syntheses of two types of fully blocked ribonucleoside 3′-phosphotriesters 6–14 have been achieved in excellent yields from 2′-O-t-butyldimethylsilyl-5′-O-monomethoxytrityl-ribonucleosides 1–5 by phosphorylation with 2-chloro- and 2,5-dichlorophenylphosphorodichloridate respectively and subsequent treatment by cyanoethanol to 6 , 8 , 10 , 12 and 14 and by p-nitrophenylethanol to 7 , 9 , 11 and 13 . These phosphotriesters are valuable starting materials for oligonucleotide syntheses due to the fact that the corresponding phosphotriesters 15–23 with free HO? C(5′) could be obtained by detritylation and the 3′-phosphodiester triethylammonium salts 24–32 by deblocking of the cyanoethyl and the 2,5-dichlorophenyl group respectively. All newly synthesized compounds have been characterized by UV.-and NMR.-spectra as well as C, H, N elementary analyses. 相似文献
13.
It is well known that the unique 7-vertex triangulation of the 2-dimensional torus S1×S1 is a consequence of the relationship between two hexagonal lattices in the euclidean plane: it is just the quotient of the triangular tessellation of the plane by a translation group. Each vertex star is a regular hexagon and the symmetry group of this triangulation is the affine group A(1,7) in one dimension over 7. In this paper we describe a particular 15-vertex triangulation of the 3-dimensional torus S1×S1×S1 whose symmetry group is the affine group A(1,15) and which is similarly related to two lattices in euclidean 3-space: it is just the quotient of a particular tessellation of 3-space by a translation group. Each vertex star happens to be a rhombidodecahedron, the dual of a (semiregular) cuboctahedron. 相似文献
14.
Extracting organotin compounds (OTC) from soils is difficult due to the high cation exchange and complexation capacity of soils, and little information about OTC in soils is available. In this study, a new extraction method, combining 1 M CaCl2, 0.1% tropolone, and glacial acetic acid was developed. Recoveries of mono-substituted OTC from spiked plant litter, and soil samples were improved substantially to 40% compared to classical glacial acetic acid extraction commonly used in sedimentology, yielding <10% recovery in C-rich soil samples. Simultaneously, the recovery of other OTC, trimethyllead and monomethylmercury was satisfactory. The recoveries of most species from the spiked litter, upland and wetland soils exceeded 70%. The new method extracted much more organometallics from unspiked organic soils and litter than microwave- and ultrasound-assisted extraction and accelerated solvent extraction, most likely due to exchange of organometallics from the solid phase by Ca2+. The method is simple, highly efficient and with low contamination. Together with GC-ICP-mass spectrometry, the method allows the detection of these organometallics in the pg g−1 range and it is particularly suitable for soil and plant materials with low organometallics contents. 相似文献
15.
Reaction of the cyclic 1, 3-dicarboxylic acid derivatives (), () and () with (R)- or (S)-citronellal (/) gives the enantiomeric tricyclic dihydropyrans (), (), () and (), probably via a 100% stereocontrolled intramolecular cycloaddition. 相似文献
16.
Enantioselective C-P cross-coupling of diarylphosphines and ortho-substituted aryl iodides has been achieved with >90%ee, using an in situ catalyst prepared from Et,Et-FerroTANE, Pd(2)(dba)(3) x CHCl(3) and LiBr. 相似文献
17.
Serge Mignani Francis Lahousse Robert Merényi Zdenek Janousek Heinz Gunter Viehe 《Tetrahedron letters》1985,26(38):4607-4608
Carbanions carrying captodative substitution are readily oxidized to their dimers. 相似文献
18.
We consider the problem of the existence of convergent series solutions for partial differential operators of the form
. We give first conditions for P such that the linear equation Pu=f has an analytic solution, then we solve nonlinear equations of the form Pu=F(x,u). For applications we treat also cases with parameters and give a proof of a theorem of S. Kaplan [5]. In the last section we consider a case where small denominators occur. 相似文献
19.
Acidity constants of six substituted 1-benzyl-1-methoxy-2-nitroethylenes (2-Z with Z = m-NO(2), m-CF(3), m-Cl, H, p-Me, p-MeO) and their respective nitronic acids were determined in 50% DMSO-50% water (v/v) at 20 degrees C. Kinetic data were obtained on the reversible deprotonation of all six 2-Z by OH(-) and piperidine and on the reversible deprotonation of 2-NO(2)() by piperazine, 1-(2-hydroxyethyl)piperazine, and morpholine in the same solvent. These data allowed a determination of the Br?nsted coefficients alpha (dependence on acidity of 2-Z) and beta (dependence on amine basicity). The fact that alpha > beta indicates the presence of a transition state imbalance which, however, is much smaller than that for the deprotonation of arylnitromethanes. The reasons for this reduction in the imbalance and their relevance to a recent study of the deprotonation of Fischer carbene complexes are discussed. 相似文献
20.
Dr. Christiane Stoll Prof. Dr. Mihail Atanasov Jascha Bandemehr Prof. Dr. Frank Neese Clemens Pietzonka Prof. Dr. Florian Kraus Prof. Dr. Antti J. Karttunen Dr. Markus Seibald Assoc. Prof. Dr. Gunter Heymann Prof. Dr. Hubert Huppertz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(38):9801-9813
As a consequence of the static Jahn-Teller effect of the 5E ground state of MnIII in cubic structures with octahedral parent geometries, their octahedral coordination spheres become distorted. In the case of six fluorido ligands, [MnF6]3− anions with two longer and four shorter Mn−F bonds making elongated octahedra are usually observed. Herein, we report the synthesis of the compound K3[MnF6] through a high-temperature approach and its crystallization by a high-pressure/high-temperature route. The main structural motifs are two quasi-isolated, octahedron-like [MnF6]3− anions of quite different nature compared to that met in ideal octahedral MnIII Jahn-Teller systems. Owing to the internal electric field of Ci symmetry dominated by the next-neighbour K+ ions acting on the MnIII sites, both sites, the pseudo-rhombic (site 1) and the pseudo-tetragonally elongated (site 2) [MnF6]3− anions are present in K3[MnF6]. The compound was characterized by single-crystal and powder X-ray diffraction, and magnetometry as well as by FTIR, Raman, and ligand field spectroscopy. A theoretical interpretation of the electronic structure and molecular geometry of the two Mn sites in the lattice is given by using a vibronic coupling model with parameters adjusted from multireference ab-initio cluster calculations. 相似文献